A vehicle crash sensing system detects and discriminates severe crash events which require deployment of an airbag, from minor crash incidents which do not. Discrimination is accomplished by means of an on-board accelerometer and associated signal processing algorithm contained within a microprocessor. Since the total available time for deploying an airbag to effectively restrain occupants in a severe crash event is very short, the ability to quickly and reliably determine the severity of a collision is paramount. Equally important is system immunity to inadvertent deployment during minor crash incidents, one category of which are rough road events.
Prior art airbag deployment algorithms have been developed which utilize one or more quantities for measuring the severity of a collision. One such quantity is vehicle velocity change, calculated as an integral of vehicle deceleration data generated by the accelerometer. FIG. 1 illustrates a graph of vehicle velocity change curves for various types of rough road events. These events include 40 km/h pothole 10; 96 km/h chatterbumps 12; 48 km/h square block road 14; 9 km/h curb impact 16; and 32 km/h curb dropoff 18. FIG. 2 illustrates a graph of vehicle velocity change curves for various types of severe crash events. These events include a 30 mph frontal barrier 20; 30 mph, 30.degree. angle barrier 22; 30 mph center pole 24; and 13 mph from barrier 26.
Comparing FIGS. 1 and 2, it can be observed that the vehicle velocity change curves of rough road events are much more "wavy" than those of severe crash events. Them is a desire to quantify the "waviness" or oscillatory content of vehicle velocity change curves for accurately detecting the presence of a rough road surface.